Many protozoa live in the human body. Many of them are pathogenic. Our story is about ten of them, most of them. The review is based on both historical and current publications.
largest. BalantidiumBalantidium coli
The largest protozoon is a human parasite and the only ciliate in this company. Its dimensions vary from 30 to 150 micrometers in length and from 25 to 120 micrometers in width. For comparison: the length of the malaria plasmodium in the largest stage is about 15 micrometers and is many times less than the balantidium of the intestinal cells under which the infusoria live. An elephant in a china shop.
Distributedwherever there are pigs - the main porters. Usually lives in the submucosa of the large intestine, although it is also found in the lung epithelium in humans. It feeds onB. colibacteria, food particles and fragments of the host epithelium. In animals, the infection is asymptomatic. People can develop severe diarrhea with a bloody, slimy discharge (balantidiasis), and sometimes ulcers form in the walls of the colon. It is rare to die from balantidiasis, but it causes chronic fatigue.
People are infected by dirty water or foods that contain cysts. The infection rate in humans does not exceed 1%, while pigs can be infected all over the world.
Treated with antibioticsno reports of drug resistance of this ciliate have yet been published.
Discovered by the Swedish scientist Malstem in 1857. Balantidiasis today is associated with tropical and subtropical areas, poverty and poor hygiene.
The very first. Oral amoebaEntamoeba gingivalis
The first parasitic amoeba to be found in humans. The description of the amoeba was published in the oldest scientific journal in 1849. Amoeba found in plaque, hence the name from the Latin gingiva - gums.
Livesin the mouth of almost everyone with aching teeth or gum pain, inhabits gum pockets and plaque. It feeds on epithelial cells, leukocytes, microbes and, in the case of erythrocytes. It's rare in people with a healthy oral cavity.
This small protozoon with a size of 10 to 35 µm does not get into the environment and does not form cysts. It is transmitted to another host through kissing, dirty dishes, or contaminated food. E. gingivalisis considered a purely human parasite, but is sometimes found in captive cats, dogs, horses, and monkeys.
In the early twentieth century,E. gingivaliswas described as causing periodontitis because it is always present in inflamed tooth cells. However, the pathogenicity has not been demonstrated.
The drugsthat affect this amoeba are unknown.
Most widely used. Dysentery amoebaEntamoeba histolytica
This intestinal parasite with blood invades the tissues of the liver, lungs, kidneys, brain, heart, spleen and genitals. He eats what he gets: food particles, bacteria, erythrocytes, leukocytes and epithelial cells.
Distributed everywhere, especially in the tropics. Usually, people get infected by swallowing a cyst.
In temperate countries, the amoeba remains in the intestinal lumen and the infection is asymptomatic. The pathological process often begins in the tropics and subtropics:E. histolyticaattacks the walls. The reasons for the transition to the pathogenic form are still unclear, but several molecular mechanisms behind it have already been described. So it is clear that amoeba secrete lysing substances, break through the mucus and kill cells. Apparently the amoeba can destroy the host cell in two ways: by triggering apoptosis or simply by chewing pieces off. The first method has long been considered the only one. By the way, the mechanism of cellular suicide at a record speed - in minutes - has not been identified. The second method was only recently described, the authors called it trogocytosis from the Greek "three" - to gnaw. It is noteworthy that the cell-biting amoeba leave their prey as soon as it dies. Others can completely phagocytize dead cells. It is believed that biting and devouring cells differ in the pattern of gene expression.
Now the amoeba's ability to invade the bloodstream, liver, and other organs is linked to trohocytosis.
Amebiasis is a deadly disease. Every year around 100, 000 people die from an infection withE. histolytica.
The dysentery amoeba has a non-pathogenic twin,E. dispar, so microscopy is not sufficient to diagnose the disease.
For healing, the mobileE. histolytica must be destroyedand cysts.
DescribedE. histolyticaand determined its pathogenic nature in a patient with diarrhea in 1875. The Latin name for amoeba was given in 1903 by the German zoologist Fritz Schaudin.Histolyticameans tissue-destroying. In 1906 the scientist died of an amoebic bowel abscess.
Most common. Intestinal lamblieGiardia lamblia (G. intestinalis)
Giardia, the most common intestinal parasite, is ubiquitous. 3-7% of people in developed countries and 20-30% in developing countries are infected. That's about 300 million people.
The parasites livein the duodenum and bile ducts of the host, where they float, work with flagella and then attach themselves to the epithelium with the help of a sticky disc on the underside of the cell. For 1 cm2the epithelium adheres to a million lamblia. They damage the villi, which affects the absorption of nutrients and causes inflammation of the mucous membranes and diarrhea. When the disease affects the biliary tract, it is associated with jaundice.
Giardiasis is a disease of dirty hands, water, and food. The life cycle of a protozoa is simple: there is an active form in the intestine and at the exit there are stable cysts with fecal masses. To become infected, it is enough to swallow a dozen cysts, which turn back into an active form in the intestines.
The main secretof the ubiquity of lamblia in the variability of surface proteins. The human body fights against lamblia with antibodies and is in principle able to develop immunity. But people who live in the same area and drink the same water keep getting infected by the offspring of their own parasites. Why? Because during the transition from the active phase to the cyst and vice versa, lamblia changes the proteins against which antibodies are produced - variant-specific surface proteins. There are around 190 variants of these proteins in the genome, but only one is ever present on the surface of a single parasite, translation of the rest is disrupted by the mechanism of RNA interference. And the change happens roughly every ten generations.
It is treatedwith an antiprotozoal agent with antibacterial activity. The disease goes away in a week, but if the biliary tract is infected, relapses are possible for many years. Cysts are fought by iodising water.
Discovered by the Czech scientist Vilém Lambl in 1859Giardia lamblia. Since then, the simplest has changed several names and the current one has been given in honor of the explorer and French parasitologist Alfred Giar, who did not describe Lamblia.
And the first sketch of Giardia was done by Anthony van Leeuwenhoek, who found it in his own angry chair. It was in 1681.
Giardia is also very evolutionarily old, it comes almost directly from the ancestor of all eukaryotes.
The most intimate. Trichomonas vaginalisTrichomonas vaginalis.
The simplest one that is sexually transmitted. It lives in the vagina and in men - it is transmitted sexually or through damp washcloths in the urethra, epididymis, and prostate. Babies can become infected through the birth canal.T. vaginalishas 4 flagella at the front end and a relatively short, undulating membrane that releases pseudopods when needed. The maximum size of Trichomonas is 32 by 12 microns.
Trichomonas ismore commonthan the causative agents of chlamydia, gonorrhea and syphilis combined. It affects around 10% of women and possibly more and 1% of men. The latter number is unreliable because it is more difficult to spot the parasite in men.
T. vaginalisfeeds on microorganisms, including lactic acid bacteria of the vaginal microflora, which maintain an acidic environment, creating an optimal pH for itself above 4. 9.
Trichomonas destroys cells of the mucous membrane and causes inflammation. About 15% of infected women complain of symptoms.
It is treatedwith an antibacterial drug. As a preventive measure, regular showering with diluted vinegar is recommended.
Described in 1836 by the French bacteriologist Alfred Donne. The scientist did not understand that there was a pathogenic parasite in front of him, but he determined the size, appearance and type of movement of the simplest.
The deadliest. The causative agent of sleeping sicknessTrypanosoma brucei
The African sleeping sickness pathogen is the deadliest protozoon. A person infected with it dies without treatment. The trypanosome is an elongated flagellate 15 to 40 µm in length. There are two subspecies that cannot be distinguished externally. Disease caused byT. brucei gambiense, lasts 2-4 years.T. brucei rhodesienseis a more virulent, temporary pathogen from which they die after a few months or weeks.
Distributedin Africa between the 15th parallels of the southern and northern hemisphere in the natural area of the carrier - blood-sucking insects of the genusGlossina(tsetse fly). Of the 31 fly species, 11 are dangerous to humans. Sleeping sickness affects the population of 37 countries south of the Sahara 9 million km away2. Up to 20, 000 people fall ill every year. Now there are about 500, 000 patients, 60 million are at risk.
From the fly bowelT. bruceienters the human bloodstream, from there into the cerebrospinal fluid and influences the nervous system. The disease begins with fever and inflammation of the lymph glands, followed by lethargy, drowsiness, muscle paralysis, exhaustion, and irreversible coma.
The lethality of the parasite is related to its ability to cross the blood-brain barrier. The molecular mechanisms are not fully understood, but the parasite is known to secrete cysteine proteases upon entering the brain and also to use some host proteins. In the central nervous system, however, the trypanosome protects against immune factors.
The first description of sleeping sickness in the upper reaches of the Niger was left by the Arab scholar Ibn Khaldun (1332-1406). As early as the early 19th century, Europeans were aware of the first signs of the disease - swelling of the lymph nodes in the neck (a symptom of Winterbottom), and slave traders paid special attention to it.
DiscoveredT. bruceiThe Scottish microbiologist David Bruce, after whom she is named, first established the connection between trypanosome, tsetse fly and sleeping sickness in 1903.
Treatmentdepends on the stage of the disease, and medication causes serious side effects. The parasite has high antigen variability, making it impossible to make a vaccine.
The most extravagant. LeishmaniaLeishmania donovani
Leishmanias have earned the title of the most extravagant parasites because they live and multiply in macrophages - cells designed to destroy parasites.L. donovaniis the most dangerous of them. It causes visceral leishmaniasis, colloquial dumdum fever, or kala azar, from which almost all patients die without treatment. But the survivors acquire long-term immunity.
There are three subspecies of the parasite.L. donovani infantum(Mediterranean and Central Asia) mainly affects children, dogs are often its reservoir.L. donovani donovani(India and Bangladesh) is dangerous for adults and the elderly and has no natural reservoirs. The AmericanL. donovani chagasi(Central and South America) can live in the blood of dogs.
L. donovani- Flagellate no longer than 6 microns. People become infected after being bitten by mosquitoes of the genusPhlebotomus, sometimes through sexual contact, babies - who go through the birth canal. In the blood,L. donovanipenetrates the macrophages that carry the parasite through the internal organs. The parasite multiplies in macrophages and destroys them. The molecular survival mechanism in macrophages is quite complex.
Disease symptoms- fever, enlarged liver and spleen, anemia and leukopenia, which contribute to the secondary bacterial infection. Every year 500, 000 people develop visceral leishmaniasis and around 40, 000 die.
Treatmentheavy - intravenous antimony and blood transfusion.
Taxonomic affiliationL. donovaniwas defined in 1903 by the famous malaria researcher and Nobel Prize winner Ronald Ross. It owes its generic name to William Leishman and the specific name to Charles Donovan, who in 1903 independently discovered protozoan cells in the spleen of patients who died of Kala Azar, one in London, the other in Madras.
The most difficult life cycle.Babesia spp.
Babesia, in addition to multi-stage asexual reproduction in mammalian erythrocytes and sexual mites in the intestine of the genusIxodes, have made their development more difficult through transovarial transmission. Protozoal sporozoites penetrate the ovaries from the intestines of a female mite and infect embryos. When the mite larvae hatch, babesia invade their salivary glands and enter the vertebrate's blood at the first bite.
DistributedBabesia in America, Europe and Asia. Their natural reservoirs are rodents, dogs and cattle. A person is infected with several types: B. microti, B. divergens, B. duncaniandB. venatorum.
The symptoms of babesiosis are similar to malaria - recurrent fever, hemolytic anemia, enlarged spleen and liver. Most people recover spontaneously, but babesiosis is fatal in those with compromised immune systems.
Treatment methodsare still being developed while antibiotics and, in severe cases, blood transfusions are being prescribed.
Babesia was described by the Romanian microbiologist Victor Babes (1888), who discovered it in sick cows and sheep. He decided it was a pathogenic bacterium, which he namedHaematococcus bovis. Babesia was considered an animal pathogen for a long time until it was discovered in 1957 in a Yugoslav shepherd who died of an infection with B. divergens.
The most influential. The causative agent of toxoplasmosisToxoplasma gondii
T. gondiiis the strongest parasite because it controls the behavior of intermediate hosts.
Distributed everywhere, unevenly distributed. For example, in France 84% of the population are infected and in the UK 22%.
The life cycle of Toxoplasma consists of two phases: Asexually, all warm-blooded sexual reproduction occurs in the body that is only possible in the epithelial cells of the cat's intestine. ToT. gondiicould complete the development, the cat has to eat an infected rodent. By making this event more likely,T. gondiiblocks rodents' natural fear of the smell of cat urine and makes it attractive by targeting a group of neurons in the amygdala. How she does this is unknown. One of the suspected mechanisms of action is a local immune response to an infection. It changes cytokine levels, which in turn increases levels of neuromodulators like dopamine. Toxoplasma also affects human behavior, which manifests itself even at the population level. In countries with high levels of toxoplasmosis, neuroticism and a desire to avoid unsafe new situations are more common. It is possible thatT. gondiiinfection can lead to cultural changes.
Infectionin humans is often asymptomatic, but if immunity is weakened it destroys cells of the liver, lungs, brain and retina and causes acute or chronic toxoplasmosis. The course of infection depends on the virulence of the strain, the state of the host's immune system and its age - the elderly are less prone to thisT. gondii.
Treattoxoplasmosis with antiprotozoal drugs.
Describedin 1908 on desert rodents. This award belongs to the staff of the Pasteur Institute in Tunisia, Charles Nicolas and Luis Manso.
Most pathogenic. Plasmodium malariaPlasmodium spp.
Plasmodium malaria is the most pathogenic parasite in humans. The number of malaria patients can reach 300 to 500 million, the death rate from epidemics 2 million. The disease still claims three times more lives than armed conflict.
Five types of Plasmodium cause malaria in humans:Plasmodium vivax, P. falciparum, P. malariae, P. ovaleandP. knowlesi, which also affect macaques.
Distributedin the area of the vectors - mosquitoesAnopheles, which require a temperature of 16–34 ° C and a relative humidity of more than 60%.
A comparison of the genome of the most virulent plasmodia,P. falciparum, with gorilla plasmodia suggests that humans from their ancestors were infected by these monkeys. The emergence of this form of Plasmodium is linked to the emergence of agriculture in Africa, which led to an increase in population density and the development of irrigation systems.
Plasmodia reproduce sexually in the intestines of mosquitos, and in the human body it is an intracellular parasite that lives in hepatocytes and erythrocytes and reproduces until the cells burst. 1 ml of patient blood contains 1 - 50, 000 parasites.
The disease manifests itself in inflammation, recurrent fever and anemia. In the event of pregnancy, it is dangerous for both mother and fetus. Erythrocytes infected withP. falciparumclog the capillaries, and in severe cases, ischemia of internal organs and tissues develops.
The treatmentrequires a combination of several drugs and depends on the specific pathogen. Plasmodia become resistant to drugs.